The operating systems of computers require that file names meet certain constraints. A common constraint is to limit the maximum number of characters in a file name. MS-DOS.RTM. operating system (MS-DOS is a registered trademark of Microsoft Corporation) limits file names to 11 characters; MACINTOSH.RTM. operating system (MACINTOSH is a registered trademark of Apple Computer, Inc.) limits file names to 31 characters; the UNIX.RTM. File System (UNIX is a registered trademark of UNIX System Laboratories, Inc.) and the OS/2.RTM. High Performance File System (OS/2 is a registered trademark of IBM) limit file names to 255 characters. Another common constraint is to restrict the set of characters that a file name may include, for example, MS-DOS systems prohibit characters such as " " (blank space) from file names, and MACINTOSH systems prohibit ":" (colon characters). MS-DOS systems also constrain file names into a format with eight-character names and three-character extensions, while other file systems permit any file name structure.
It would be desirable if users of operating systems having restrictive file naming formats were capable of accessing files created and named by other operating systems in such a way as to permit files to be shared among different operating systems. It is clearly very easy to enable operating systems having less-restrictive file naming formats to access files created by operating systems having more-restrictive file naming formats. The difficulty lies in providing access to less restrictively-named files from operating systems having more restrictive file naming formats. Since some operating systems like MS-DOS have much more restrictive file names than other operating systems, e.g., MACINTOSH and UNIX, it is possible to create and name files in less restrictive operating systems with names that are illegal in more restrictive operating systems. For example, one can create a file called "meeting agenda" on either a MACINTOSH or a UNIX file system, however this file name is illegal on MS-DOS systems because it is too long (14 characters), does not meet the 8-character-file name/3-character-extension format, and includes an illegal character (a blank space).